Commercial greases for space applications usually fulfill the requirements imposed by the severe conditions of use. The main requirement is their ability to create an EHL film, boundary film, or both under speed, load and temperature conditions that the mechanisms will operate. Three greases, all based on a multiply alkylated cyclopentane (Pennzan(R)) base oil, were studied. The thickeners were an n-octadecylterephthalamate soap, a lithium soap, and a urea derivative. A Four-Ball Tribometer and a Spiral Orbit Tribometer were employed to evaluate the greases under ultrahigh vacuum. Results indicated that all three greases yielded very low wear rates and extended lifetimes. In addition, routine physical property data is reported for each grease.